YouTube (NSDQ: GOOG) announced today that it’s getting rid of a 15-minute limit on the duration of videos uploaded by users. Ditching the limit suggests that YouTube is pretty happy with how well Content ID, a software system that prevents uploading of copyrighted works, is working.

The time limits on videos had always been imposed because of concerns by copyright holders that a barrage of full-length TV episodes or feature movies would hit the site. The 15-minute limit was imposed this summer and replaced a 10-minute limit that had been in place since at least 2006.

The change is being introduced as YouTube is moving into a stronger position on copyright issues. In June, it defeated Viacom’s $1 billion copyright infringement lawsuit. Even Viacom (NYSE: VIA) has admitted the effectiveness of Content ID as it works today, by filing motions in its lawsuit indicating that it won’t seek damages for any content hosted on YouTube after 2008.

Content ID has been in place since 2007 and works by matching uploaded content against a cache of audio and visual material provided by content owners. More than 1000 companies are using the system to manage their content on YouTube.

The lifting of time limits isn’t happening all at once. YouTube will start by rolling out an unlimited video service to “selected users with a history of complying with the YouTube Community Guidelines and our copyright rules.” Are you one of YouTube’s trusted few? You can find out by logging into the service and clicking on “Upload.”